Technical Field
[0001] The present invention relates to a white LED device for illumination, and more particularly,
to a white LED device for illumination with high color rendering properties using
a blue LED chip having high luminance as an excitation light source.
Background Art
[0002] EP 2 056 366 A discloses a LED lamp wherein emission from the blue LED element is dominant for light
emission in the wavelength region from 380 to 475 nm, emission from the first fluorescent
material is dominant for light emission in the wavelength region from 475 to 520 nm,
emission from the second fluorescent material is dominant for light emission in the
wavelength region from 520 to 560 nm, emission from the third fluorescent material
is dominant for light emission in the wavelength region from 560 to 615 nm, and emission
from the fourth fluorescent material is dominant for light emission in the wavelength
region from 615 to 780 nm.
[0003] US 6,621,211 B2 discloses a white light illumination system comprising a light emitting diode, a
first luminescent material having a peak emission wavelength of about 575 to about
620 nm, and a second luminescent material having a peak emission wavelength of about
495 to about 550 nm, which is different from the first luminescent material, a third
luminescent material having a peak emission wavelength of about 420 to about 480 nm,
which is different from the first and second luminescent material, and a fourth luminescent
material having a peak emission wavelength of about 620 to about 670 nm.
[0004] US 2007/0278935 A1 discloses a first type of the phosphors having a fluorescence peak wavelength of
not less than 400 nm and less than 500 nm, a second type of phosphors having a fluorescence
peak wavelength of not less than 500 nm and less than 600 nm, and a third type of
the phosphors having a fluorescence peak wavelength of not less than 600 nm and not
more than 700 nm dispersed therein.
[0005] EP 2 554 631 A2 discloses a light emitting diode (LED) having an emission wavelength in a range of
440 nm to 470 nm, and a phosphor composition disposed on the LED comprising: a first
yellow phosphor having a peak wavelength in a range of 535 nm to 545 nm, a second
yellow phosphor having a peak wavelength in a range of 545 nm to 555 nm, and a red
phosphor having a peak wavelength in a range of 645 nm to 655 nm, wherein a range
of chromaticity coordinated of the white light is CIE x 0,25 to 0,3 and CIE y: 0,22
to 0,28.
[0006] With the commercialization of blue LEDs in the late 1990s, white LED devices have
appeared, which employ a phosphor such as YAG (Yttrium Aluminum Garnet) for emitting
yellow light by absorbing the excitation light at the corresponding wavelength using
a blue LED chip as an excitation light source. This white LED has high luminance but
is problematic because the wavelength interval between blue and yellow is wide, thus
making it difficult to achieve mass production of white LEDs having the same color
coordinates due to the scintillation effect by the color separation. Furthermore,
it is very difficult to adjust color temperature (CT) and color rendering index (CRI),
which are regarded as important in a light source for illumination. The CRI of typical
white LEDs is only 75 ∼ 80.
[0007] Hence, white LED devices have been developed by applying an R/G/B multilayer fluorescent
material on a UV LED chip to thus exhibit superior color stability and a wide emission
spectrum as in incandescent bulbs. CT and CRI in such white LEDs are easy to adjust
and thus white LEDs are receiving attention as a light source of an LED for illumination
(Japanese Patent Application Publication No.
2002-171000). However, this patent is problematic because the white LED using the UV chip as
an excitation light source has low luminance, compared to white LED devices using
blue LED chips.
[0008] In addition, methods of emitting white light by combining multiple LED chips such
as R/G/B have been proposed, but have drawbacks, such as non-uniform driving voltage
per chip, and changes in the power of chips depending on the ambient temperature,
which thus produces different color coordinates.
[0009] Although a variety of methods have been devised to achieve white LEDs as mentioned
above, thorough research is ongoing into white LEDs using green and red phosphors
instead of the yellow phosphor, with the use of a blue LED as an excitation light
source due to high luminance of the blue LED (Korean Patent Application Publication
No.
2008-0063709). In this case, color reproducibility may be increased to some extent, but is still
insufficient. For example, a white LED lamp including green and red phosphors has
low CRI for specific colors such as R9 (Red) or R12 (Blue).
[0010] Furthermore, because of instability of the material for the phosphor, such as damage
to the red or green phosphor of the white LED device due to external energy or the
like, unreliable products may result.
Disclosure
Technical Problem
[0011] Accordingly, the present invention has been made keeping in mind the problems encountered
in the related art, and the present invention is intended to provide a high color-rendering
white LED chip using a blue LED chip as an excitation light source.
[0012] In addition, the present invention is intended to provide a white light emitting
device, which may emit white light close to natural light by optimizing the composition
and mixing ratio of individual phosphors to achieve high color rendering properties
and high light luminance.
Technical Solution
[0013] The present invention provides a white light emitting device, comprising a blue LED
chip having an excitation wavelength of 440 - 460 nm and a phosphor layer excited
by the excitation wavelength of the blue LED chip to emit light, wherein the phosphor
layer comprises: a first phosphor powder chemical formula of (Ba,Eu)Si
x(O,Cl)
xN
x (1 < x < 5), and the first phosphor powder having an emission peak wavelength of
480 ∼ 499 nm; a second phosphor powder of at least one phosphor selected from a group
of (Sr,Ba,Ca)
xSiO
2x:Eu (1 < x < 5), Si
6-yAl
yO
yN
8-y:Eu (0.1 < y < 0.5), and Al
8-zLu
zO
12:Ce
++ (1< z < 5), the second phosphor powder_having an emission peak wavelength of 500
- 560 nm; and a third phosphor powder of at least one phosphor selected from a group
of (Sr,Ca) AlSiN
x:Eu (1 < x < 5), and CaAlSiN
y:Eu (1 < y < 5), the third phosphor having an emission peak wavelength of 600 ∼ 650
nm, wherein the white light emitting device has an average color rendering index of
over 90% or more and a color rendering index R9 of 90% or more.
[0014] Preferably, the white light emitting device has an average color rendering index
of 90% or more and R12 of 90% or more.
[0015] Also, the white light emitting device may have a peak wavelength in the range of
485 - 504 nm in an emission spectrum.
[0016] The white light emitting device has three peak wavelengths in different wavelength
bands in the emission spectrum.
Advantageous Effects
[0017] According to the present invention, a high color-rendering white LED chip using a
blue LED chip as an excitation light source can be provided. The white LED chip can
exhibit high color rendering properties for specific colors such as R9 and R12.
[0018] Also, the wavelength band and the mixing ratio of individual phosphors can be appropriately
adjusted with the use of a blue LED chip as an excitation light source, thus achieving
high color rendering properties including both R9 and R12 of 90% or more, making it
possible to provide an LED device for emitting light close to solar light.
Description of Drawings
[0019]
FIG. 1 illustrates a white LED device according to a preferred embodiment of the present
invention;
FIG. 2 illustrates Examples 1 to 12 for a white LED device according to the present
invention;
FIG. 3 illustrates Comparative Examples 1 to 12 for a white LED device for comparison
with the present invention;
FIG. 4 illustrates the results of evaluation of color rendering properties of Examples
1 to 12 according to the present invention;
FIG. 5 illustrates the results of evaluation of color rendering properties of Comparative
Examples 1 to 12;
FIG. 6 illustrates the emission spectra of Comparative Example 1 and Example 1 according
to the present invention;
FIG. 7 illustrates the emission spectra of Comparative Example 3 and Example 3 according
to the present invention;
FIG. 8 illustrates the emission spectra of Comparative Example 5 and Example 5 according
to the present invention;
FIG. 9 illustrates the emission spectra of Comparative Example 7 and Example 7 according
to the present invention;
FIG. 10 illustrates the emission spectra of Comparative Example 9 and Example 9 according
to the present invention;
FIG. 11 illustrates the emission spectra of Comparative Example 11 and Example 11
according to the present invention; and
FIG. 12 illustrates the overall emission spectra of FIGS. 6 to 11.
Best Mode
[0020] To fully understand the present invention, the advantages in the operation of the
present invention, and the objects accomplished by the implementations of the present
invention, reference should be made to exemplary embodiments of the present invention.
[0021] In the following description of the present invention, detailed descriptions of known
constructions and functions incorporated herein will be omitted when it may make the
subject matter of the present invention unclear.
[0022] FIG. 1 illustrates a white LED device according to a preferred embodiment of the
present invention.
[0023] As illustrated in FIG. 1, an LED device 100 includes a base substrate 110 and an
LED chip 130 mounted thereon. The LED device 100 is bonded onto a metal-based substrate
(metal PCB) 200 by a ball grid array 210 using surface mount technology (SMT), thus
forming an LED package. This package structure shows an exemplary embodiment that
employs the LED device according to the present invention, and the present invention
may be applied to the other packaging methods.
[0024] Provided on the base substrate 110 of the LED device 100 is a frame 170 having a
predetermined shape, for example, a cylindrical shape, and the inner surface of the
frame is provided with a reflector for efficiently reflecting light emitted from the
LED chip 130. Although not shown, one electrode of the LED chip 130 may be electrically
connected to a frame 170 by means of a bonding wire. Also, the other electrode of
the LED chip 130 may be electrically connected to a metal wire on the base substrate.
[0025] The LED chip 130 includes a light emitting diode having a peak wavelength of 440
∼ 460 nm. The light emitting diode may include for example an InGaN- or GaN-based
light emitting diode. Instead of the LED chip, the other light emitting device such
as a laser diode may be used in the present invention, which will be apparent to those
skilled in the art.
[0026] The LED chip 130 is covered with a phosphor layer 150. The phosphor layer 150 includes
at least three phosphors 152, 153, 154 having different emission peak wavelengths,
which are excited by the emission wavelength of the LED chip 130 to emit light at
a predetermined wavelength. In the present invention, the phosphors are preferably
provided in the form of powder. To this end, the phosphor layer 150 may include a
transparent resin for dispersing and fixing the phosphor and sealing the LED chip
130.
[0027] In the present invention, the transparent resin may include typical silicone resin
or epoxy resin.
[0028] In the present invention, the phosphors 152, 153, 154 have different fluorescent
material compositions and thus exhibit different emission peak wavelengths. Preferably,
the phosphors 152, 153, 154 include at least three fluorescent materials having different
emission wavelengths in the range of 480 ∼ 650 nm. In an embodiment of the present
invention, the phosphors 152, 153, 154 include a first phosphor B for emitting blue
light, a second phosphor G for emitting green light, and a third phosphor R for emitting
red light, after having been excited by light emitted from the LED chip. In the present
invention, the first, the second and the third phosphor are preferably composed of
an oxide or a nitride.
[0029] In the present invention, the first phosphor is excited by light emitted from the
LED chip 130, thus emitting light having a peak wavelength in the range of 480 ∼ 499
nm. The emission peak wavelength of the first phosphor is greater than the peak wavelength
of light emitted from the LED chip 130.
[0030] In the present invention, the first phosphor B, which is a phosphor for emitting
blue light, preferably includes a fluorescent material represented by Chemical Formula
1 below.
(Chemical Formula 1) (Ba,Eu)Si
x(O,Cl)
xN
x (1 < x < 5)
[0031] In the present invention, the second phosphor is excited by light emitted from the
LED chip 130, thus emitting light having a peak wavelength in the range of 500 ∼ 560
nm. The second phosphor, which is a phosphor for emitting green light, may include
fluorescent materials represented by Chemical Formulas 2 to 4 below, which may be
used alone or in combination.
(Chemical Formula 2) (Sr,Ba,Ca)
xSiO
2x:Eu (1 < x < 5)
(Chemical Formula 3) Si
6-yAl
yO
yN
8-y:Eu (0.1 < y < 0.5)
(Chemical Formula 4) Al
8-zLu
zO
12: Ce
++ (1< z < 5)
[0032] In the present invention, the third phosphor is excited by light emitted from the
LED chip 130, thus emitting light having a peak wavelength in the range of 600 - 650
nm. The third phosphor may include fluorescent materials represented by Chemical Formulas
5 and 6 below, which may be used alone or in combination.
(Chemical Formula 5) (Sr,Ca)AlSiN
x:Eu (1 < x < 5)
(Chemical Formula 6) CaAlSiN
y:Eu (1 < y < 5)
[0033] Below is a description for examples and comparative examples for a high color-rendering
white light emitting device according to the present invention and the results of
evaluation of color rendering properties thereof.
<Examples 1 to 12>
[0034] In Examples 1 to 12 according to the present invention, a first phosphor comprising
(Ba,Eu) Si
2(O,Cl)
2N
2 having an emission peak wavelength of 480 ∼ 499 nm with D50 of 15 ± 3 µm, a second
phosphor comprising Al
5Lu
3O
12;Ce
++ having an emission peak wavelength of 500 ∼ 560 nm with D50 of 12 ± 3 µm, and a third
phosphor comprising (Sr,Ca)AlSiN
3:Eu having an emission peak wavelength of 600 ∼ 650 nm with D50 of 11 ± 3 µm were
prepared.
[0035] The first phosphor, the second phosphor, the third phosphor and a silicone resin
were mixed at a mixing ratio as shown in FIG. 2, thus obtaining a sludge, which was
then applied on a blue LED chip and thermally treated at 150 ∼ 180°C to cure the silicone
resin, thereby manufacturing a white LED device as illustrated in FIG. 1. In Examples
1, 3, 5, 7, 9 and 11, an LED chip having an emission peak wavelength of 440 ∼ 450
nm was used, and in Examples 2, 4, 6, 8, 10 and 12, an LED chip having an emission
peak wavelength of 450 ∼ 460 nm was employed.
<Comparative Examples 1 to 12>
[0036] In Comparative Examples 1 to 12, a first phosphor comprising (Ba,Eu)Si
2(O,Cl)
2N
2 having an emission peak wavelength of 430 - 470 nm was prepared, and second and third
phosphors having the same emission peak wavelengths and compositions as in Examples
1 to 12 were prepared.
[0037] The first phosphor, the second phosphor, the third phosphor and a silicone resin
were mixed at a mixing ratio as shown in FIG. 3 thus obtaining a sludge, which was
then applied on a blue LED chip and thermally treated at 150 ∼ 180°C to cure the silicone
resin, thereby manufacturing a white LED device as illustrated in FIG. 1. In Comparative
Examples 1, 3, 5, 7, 9 and 11, an LED chip having an emission peak wavelength of 440
∼ 450 nm was utilized, and in Comparative Examples 2, 4, 6, 8, 10 and 12, an LED chip
having an emission peak wavelength of 450 ∼ 460 nm was used.
[0038] The white light emitting devices of Examples 1 to 12 and Comparative Examples 1 to
12 were measured for color rendering properties.
[0039] FIG. 4 illustrates the results of evaluation of the color rendering properties of
the white light emitting devices of Examples 1 to 12, and FIG. 5 illustrates the results
of evaluation of the color rendering properties of the white light emitting devices
of Comparative Examples 1 to 12.
[0040] In FIGS. 4 and 5, the white LED device samples were measured for correlated color
temperature (CCT), luminance and CRI under the condition that a current of 65 mA was
applied to each device, using a CAS 140 spectrometer made by Instrument and a MCPD
system made by Otsuka Denshi according to Japanese Industrial Standard (JIS Z 8726-1990).
[0041] Based on the measurement results of FIG. 4, Examples 1 to 12 exhibited the color
rendering index Ra of 96% or more in the color temperature range from 3000K to 6500K,
and all the color indices from R1 to R15 were 90% or more, thus manifesting high color
rendering properties, which are stable and uniform. For specific colors, R9 was in
the range from 90% to 98%, and R12 fell in the range from 90% to 97%.
[0042] On the other hand, based on the measurement results of FIG. 5, Comparative Examples
1 to 12 had relatively stable Ra of 90 ∼ 94%, from which Ra was increased by 5% or
more in Examples 1 to 12 than in Comparative Examples 1 to 12. Also, in Comparative
Examples 1 to 12, some of the color indices from R1 to R15 were lowered to the level
of about 60%. For specific colors, R9 was merely in the range of about 60 ∼ 70%, and
R12 approximated to 80%. Hence, R9 and R12 in Examples 1 to 12 were much higher.
[0043] As for the emission spectra of the above examples and comparative examples, FIGS.
6 to 11 illustrate the emission spectra of Examples 1, 3, 5, 7, 9 and 11 and Comparative
Examples 1, 3, 5, 7, 9 and 11. In respective drawings, (a) shows the emission spectrum
of the comparative example, (b) shows the emission spectrum of the example, and (c)
shows the emission spectra of both of the example and the comparative example.
[0044] As illustrated in FIG. 6, Example 1 shows the much higher numeral value in the wavelength
band of 480 - 510 nm at a color temperature of 3000K, compared to Comparative Example
1.
[0045] As illustrated in FIGS. 7 and 8, the numeral values of the emission wavelength bands
corresponding to specific color indices (R9 ∼ R15) at the color temperatures of 3500K
and 4000K were much higher in Examples 3 and 5 than in Comparative Examples 3 and
5. Moreover, as illustrated in FIGS. 9 to 11, the numeral values of the emission wavelength
bands corresponding to specific color indices (R9 ∼ R15) in the color temperature
range from 5000K to 6500K were remarkably higher in Examples 7, 9 and 11 than in Comparative
Examples 7, 9 and 11.
[0046] FIG. 12 illustrates the overall results of the emission spectra of FIGS. 6 to 11,
in which (a) shows the emission spectra of the comparative examples and (b) shows
the emission spectra of the examples.
[0047] As illustrated in FIG. 12(b), the peak wavelength was formed in the range of 485
∼ 504 nm in the emission spectra of the examples according to the present invention,
whereas there was no peak wavelength in the range of 485 ∼ 504 nm in the emission
spectra of the comparative examples as shown in FIG. 12(a).
[0048] As illustrated in FIG. 12(b), three or more peak wavelengths having different wavelength
bands in the overall spectrum were formed in the examples according to the present
invention, but there were two peak wavelengths having different wavelength bands in
the overall spectrum in the comparative examples of FIG. 12(a).
[0049] Based on the emission spectrum results as above, the peak wavelengths in the range
of 485 ∼ 504 nm in the emission spectrum according to the present invention are formed,
and thereby R12 may be increased to 90% or more. Furthermore, R9 may be greatly increased
by virtue of the formation of the peak wavelengths in the range of 485 ∼ 504 nm. Consequently,
specific color rendering indices R9 to R15 may be uniformly improved.
[0050] Hence, when the phosphor including the first phosphor having a peak wavelength band
of 480 ∼ 499 nm is applied with the use of a blue LED chip having an excitation wavelength
of 440 ∼ 460 nm, the CRI may become uniform in the color temperature range from 3000K
to 6500K. Especially, R9 and R12 may be drastically improved.